Foundation mat repair

ABSTRACT

Foundation mats which have become weakened by development of void spaces between the mat and the underlying soil are strengthened by injecting molten sulfur into the area between the mat and the soil.

United States Patent 1191 Harrison 1 1451 Oct. 29, 1974 [52] US. Cl. 61/50, 404/78 [51] Int. Cl E02d 27/08 [58] Field of Search 52/514, 744; 404/78;

[56] References Cited UNITED STATES PATENTS 1,763,219 6/1930 Christians 1. 61/36 R 1,915,032 6/1933 Poulter 404/78 1,929,215 10/1933 1,943,914 l/l934 2,227,228 12/ l 940 2,232,898 2/1941 Ackley 61/36 R Primary Examiner-W. C. Reynolds Assistant ExaminerAlex Grosz 1 5 7 ABSTRACT Foundation mats which have become weakened by development of void spaces between the mat and the underlying soil are strengthened by injecting molten sulfur into the area between the mat and the soil.

1 Claim, N0 Drawings FOUNDATION MAT REPAIR BACKGROUND AND SUMMARY OF THE INVENTION This invention relatesto a method for repairing or strengthening foundation mats which have become weakened as a result of parts of the mat having lost contact with the underlying soil and the consequent development of open space between the mat and the soil.

A foundation mat, in general, is a flat concrete slab having an extensive area and lying on a soil surface. Concrete slabs which constitute both foundation and floor of many modern houses are a species of foundation mat. Similarly, large thick concrete slabs laid on relatively soft soils to support buildings of considerable weight are a species of foundation mat. Airport runways may also be considered foundation mats though the loads they support are not constant but transient and variable, the runways being regularly subjected to sudden extremely high loadings at different points on their surfaces.

Separation of a foundation mat from the underlying soil and development of open spaces between mat and soil can come about in a variety of ways, for example, by water intrusion and flow undervthe mat, freeze-thaw cycles, mechanical shock, thermal expansion and earthquake. When once uniform, intimate contact of mat and soil is lost even in a very small area, the way is opened to more rapid loss of contact in new areas and to development of voids between mat and soil. Foundation failure becomes inevitable. When contact between the soil and a part of a foundation mat is lost, uneven loading on the soil is a necessary consequence and this leads to uneven settling of the foundation and canting of the structure it supports.

The development of void areas beneath a foundation mat which are regularly subjected to mechanical shock results in cracking of the mat and chipping of its surface. For example, an airport runway is subjected periodically to very heavy sudden impacts as aircraft touch down on the runway. If there are void spaces between the runway mat and the soil, and the impact is on the mat area lying above a void space, the mat is bent downward at the point of impact. Repeated impacts result in cracking and chipping of the concrete mat even though it is very thick. The chipped surface can be patched by recementing and smoothing but this provides only temporary relief because the patch is soon broken up by further impacts.

Pursuant to the present invention, cracking and chipping of foundation mats which have been weakened by development of void spaces between the mat and the underlying soil are prevented by injecting molten elemental sulfur into the area between the mat and the soil. Holes are drilled through the foundation mat and then molten sulfur heated to a temperature in the range 'of about ll70C is pumped at high pressure through the holes and flows along the soil surface filling void spaces between the mat and the soil. Liquid sulfur has the unusual property of decreasing in viscosity as it is cooled. For example, at lC, the viscosity of sulfur is 500 cp but when it is cooled to C, the viscosity falls to 7 cp. When sulfur at l60-l70C is pumped into the area between the soil and the mat, it cools and as it cools, its viscosity drops so that the effect of pressure drop as the sulfur flows away from the point of injection is considerably offset by the reduction in viscosity. Consequently, a large area under the mat can be reached by sulfur injected at a single point.

Both the heat capacity of liquid sulfur and the heat of fusion of sulfur are low; as a result the injected liquid sulfur sets quickly without creating heat transfer problems.

When the injected sulfur solidifies, its upper surface adheres strongly to the bottom of the mat. lts lower surfact may adhere to the underlying soil or merely rest on it depending on the character of the soil. If the soil is dry and sandy, the sulfur adheres strongly to it but if it is a moist clay then there is little adhesion. After sulfur has been injected into the area between the mat and the soil, a cross section of mat, sulfur and soil is like a sandwich in appearance, with the sulfur as a filling between an upper mat layer and a lower soil layer. The sulfur is in complete uninterrupted contact with both mat and soil, and the sulfur layer varies in thickness in the manner that'the void spaces between mat and soil had varied in thickness.

Liquid sulfur has about twice the density of water and does not mix with water. Consequently, water occupying any of the space between soil and mat is driven out of the space by the advancing sulfur flow. As a result, void spaces between soil and mat become completely ,filled with molten sulfur which then solidifies to produce a dry, coherent, strong, solid bridge between mat and soil.

I claim:

1. The method of repairing a foundation mat which has become weakened by loss of contact of parts of the mat with the underlying soil which comprises forming an opening in the mat and injecting molten sulfur at a temperature in the range l60- C. through the opening into the area between the mat and the soil. 

1. THE METHOD OF REPAIRING A FOUNDATION MAT WHICH HAS BECOME WEAKENED BY LOSS OF CONTACT OF PARTS OF THE MAT WITH THE UNDERLYING SOIL WHICH COMPRISES FORMING AN OPENING IN THE MAT AND INJECTING MOLTEN SULFUR AT A TEMPERATURE IN THE RANGE 160*-170*C. THROUGH THE OPENING INTO THE AREA BETWEEN THE MAT AND THE SOIL. 